An optical deflection element capable of scanning a light beam at an intended angle in accordance with an input signal is a fundamental element used for a variety of purposes in configuring, for instance, a laser printer, a video device such as a projector and a display, a laser scanning microscope, an optical head using optical recording, an optical diagnostic device using optical coherence tomography, a switching element for optical communication, and various sensing devices. The optical deflection element is roughly classified into mechanical deflection elements such as a vibration galvanometer, a polygon mirror, and an MEMS (Micro Electro Mechanical Systems) mirror; and non-mechanical optical deflection elements such as an acoustic-optic element and an electro-optic element.
It is difficult to miniaturize the mechanical deflection element having a mechanism for driving a mirror. High-speed scanning cannot be expected, because the mechanical deflection element requires large electric power consumption, and a mirror is used. It is possible to perform high-speed scanning by the acoustic-optic element, as compared with the mechanical deflection element. However, the acoustic-optic element includes an ultrasonic wave generation part utilizing an acoustic-optic effect. Therefore, it is difficult to miniaturize the element. Further, the drive system may be complicated and over-sized, because an elastic wave excitation signal of several hundred MHz is required.
On the other hand, in contrast to the acoustic-optic element utilizing an acoustic-optic effect, there is proposed, as an element capable of deflecting light at a high speed, an optical deflection element using an electro-optic medium (hereinafter, also referred to as “electro-optic crystal”) having an electro-optic effect (EO (Electro-Optic) effect). The performances required in the electro-optic element are capability of scanning in a wide angle, capability of scanning at a high speed, low electric power consumption or operability in response to an input signal indicating low voltage, smallness, and excellent impact resistance.
The optical deflection element using an electro-optic element controls the direction of travel of light, with use of an electro-optic effect such that the refractive index of a material changes by application of an electric field to the material. In the following, a representative conventional art using an electro-optic element is described.
There is known an electro-optic element obtained by forming a prism-shaped electrode on a surface of electro-optic crystal such as crystal of lithium niobate (LiNbO3:LN), potassium niobate (KNbO3), or potassium tantalate niobate (KTa1-xNbxO3:KTN) or by patterning a polarization inversion region such as a prism shape on electro-optic crystal. In the electro-optic element, the refractive index changes and light is deflected by applying a voltage to the electrode or to the polarization inversion region.
For instance, in patent literature 1, as illustrated in FIG. 12, a prism-shaped polarization inversion region 102 is formed on an optical waveguide layer 101 made of magnesium-oxide-doped lithium niobate and an upper electrode layer and a lower electrode layer are formed on the upper surface and the lower surface of the optical waveguide layer 101. Light deflection in a horizontal direction (xy-plane direction in FIG. 12) to the surface of the optical waveguide layer 101 is performed by applying a voltage to the upper electrode and the lower electrode.
Next, in non-patent literature 1, there is reported an optical deflection element utilizing space-charge-controlled electrical conduction, as a kind of electro-optic elements. The optical deflection effect utilizes a phenomenon, in which the refractive index change by an electro-optic element is inclined by introduction of electrons into electro-optic crystal, and wide-angle optical deflection is performed. Specifically, as illustrated in FIG. 13, optical deflection with respect to the film thickness direction (z-axis direction in FIG. 13) of a KTN crystal substrate 103 is performed by forming a metal electrode 104 on the upper surface and the lower surface of the KTN crystal substrate 103 having a large electro-optic effect, and by applying a voltage to the metal electrodes 104.
Patent literature 2 also reports an optical deflection element utilizing a space-charge-controlled electrical conduction. As illustrated in FIG. 14, the optical deflection element is configured such that two-dimensional optical deflection is performed with respect to the film thickness direction (z-axis direction in FIG. 14) of an electro-optic medium 105, and with respect to a horizontal direction (xy-plane direction in FIG. 14) to the surface of the electro-optic medium 105 by forming electrodes 106 on the upper surface and the lower surface (surfaces in parallel to xy-plane in FIG. 14) of the electro-optic medium 105, forming electrodes 107 on side surfaces (surfaces in parallel to yz-plane in FIG. 14) perpendicular to the electrodes 106, and applying a voltage between the electrodes 106 and between the electrodes 107.
Patent literature 3 also reports an optical deflection element utilizing space-charge-controlled electrical conduction. The optical deflection element is configured such that two-dimensional optical deflection is performed by growing crystal of an electro-optic medium in a solution to generate electro-optic crystal, forming electrodes on the electro-optic crystal, and applying a voltage to the electrodes.
None of the aforementioned conventional arts, however, succeeded in realizing a small-sized optical deflection element capable of two-dimensionally deflecting a light beam at a low drive voltage and at a high speed with use of one substrate.